William of Saint-Thierry, French Guillaume de Saint-Thierry (born c. 1085, Liège, Lower Lorraine—died probably Sept. 8, 1148) French monk, theologian, and mystic, leading adversary of early medieval rationalistic philosophy.

William studied under Anselm of Laon, a supporter of the philosophical theology (later called scholasticism) advanced by St. Anselm of Canterbury. After entering a Benedictine abbey in Reims in 1113, William became thoroughly versed in scriptural and patristic writings. Elected abbot of the Abbey of Saint-Thierry, near Reims, in 1119, he expressed his preference for contemplation and writing rather than ecclesiastical administration, but he remained in office at the urging of his friend Bernard of Clairvaux. During that period William wrote two works fundamental to his theological system, De natura et dignitate amoris (“On the Nature and Dignity of Love”) and De contemplando Deo (“On the Contemplation of God”). De sacramento altaris (“On the Sacrament of the Altar”), a treatise on the Eucharist, he dedicated to Bernard, who earlier had dedicated two of his own works to William.

From 1128 to 1135 William compiled several treatises and biblical commentaries attempting to synthesize the theology and mysticism of Western and Eastern Christianity, specifically an integration of the thought of St. Augustine, Origen, and Gregory of Nyssa. William’s Meditativae orationes (“Meditative Prayers”) expressed spiritual concerns with an intensity comparable to Augustine’s in his Confessions. In 1135 he withdrew to the meditative life of the Cistercian Monastery of Signy in the Ardennes, where he addressed questions of the spiritual life and the problem of faith in his Speculum fidei (The Mirror of Faith) and Aenigma fidei (“The Enigma of Faith”), written in 1144. In the same year, after visiting the Charterhouse of Mont-Dieu, near Reims, he composed the Epistola ad fratres de Monte Dei (“Letter to the Brothers of Mont-Dieu”), called the “Golden Epistle” (Eng. trans., 1930), one of the most significant medieval works on the value of the contemplative life.

Elaborating the essential elements of his doctrine on mysticism, William proposed that the soul, although alienated from God, is also intrinsically empowered to experience a mystical “return” to its divine origin during its earthly existence, a return effected in stages. Thus is man progressively liberated from his material and temporal impediments, eventually undergoing an experiential knowledge of God by a process of reminiscence, understanding, and love.

The writings of William of Saint-Thierry are contained in the series Patrologia Latina, J.-P. Migne (ed.), vol. 180 (1890). His Speculum fidei was edited in an English version, The Mirror of Faith, by Geoffrey Webb and Adrian Walker in 1959.

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...masters and by his apparent revisions of the traditional teachings of Christian theology. Within Paris the influential abbey of Saint-Victor was studiously critical of his doctrines, while elsewhere William of Saint-Thierry, a former admirer of Abelard, recruited the support of Bernard of Clairvaux, perhaps the most influential figure in Western Christendom at that time. At a council held at...